1. Field of the Invention
The present invention relates to an optical device.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2006-93359, which is hereby incorporated by reference, describes a conventional light emitting device in which LEDs are arranged in a diagonal direction (hereinafter, referred to as a diagonal LED). FIG. 1 is a schematic diagram of the light emitting device described in Japanese Patent Application Laid-Open No. 2006-93359. The light emitting device 100 of FIG. 1 has a plastic leaded chip carrier (PLCC) structure. With this structure, LED chips (e.g., blue and red LED chips 105 and 106) are attached by die bonding into a recess 102 of a package 101, which is molded with a lead frame 104 as an insert. The lead frame and the LED chips are electrically connected to each other by wire bonding with Au wires (not shown). A sealing resin 103 is then injected into the recess 102, thereby protecting the LED chips 105, 106 and the Au wires as well as bonding the lead frame 104 and the molding resin of the package 101 to each other.
Since the fabrication of the PLCC structure such as the structure shown in FIG. 1 includes insert-molding a lead flame such as the lead frame (matrix frame) 107 shown in FIG. 2 and die-bonding LED chips onto the lead frame, which has a flat shape, a step of cutting and forming the lead frame into shape is required.
The sealing resin also needs to be injected into the recess of the insert-molded package, and as a result the molding resin of the package and the sealing resin can sometimes peel off from each other.
Moreover, dicing the matrix frame 107 into individual pieces produces cutting burrs, which may result in a lifted mount. In addition to this, forming the lead frame 104 (bending the lead frame at several points into a triangular shape) can cause springback, whereby the LED may be mounted in an abnormal position.
The configuration shown in FIG. 1 entails resin molding, and it is therefore necessary to reduce the thickness of the resin if miniaturization is intended. In a reflow soldering step, however, the housing (package 101) is subjected to temperatures as high as 260° C. or more. Resins that are resistant to these high temperatures even with a low profile are limited to such special resins as LCP (liquid crystal polymer) and PEEK (polyetheretherketone), which require different conditions than in typical resin molding, including molding temperature and pressure. PPA (polyphthalamide), nylon 9T, and other resins that have high reflectance in the visible light region in particular tend to exceed their allowable temperatures for thermal deformation, and thus are difficult to use. Fillers can surely be added into the resins for the purpose of increasing the allowable temperature limits. However, adding fillers lowers the reflectances of the resins, and makes their molding conditions including temperature, injection speed, and injection pressure more difficult to adjust than those of ordinary resins. Furthermore, due to the drop in flowability of resins resulting from adding fillers, there has been a problem that the resins are not usable for diagonal LEDs of small size, which require molding of small thicknesses.
Furthermore, if the device is miniaturized, and the LEDs are enhanced in output and reduced in wavelength, then the resin material of the housing (the package 101) undergoes even higher irradiation and higher photon energy, causing a drop in reflectance due to photo-degradation. The resulting specular change makes a drop in output greater than with light emitting diodes of longer wavelengths, thereby contributing to variations between the outputs of different wavelengths within the same package.
For the sealing resin 103, a silicone resin or a modified silicone-epoxy resin resistant to short wavelengths is used. Despite being resistant, the sealing resin peels off due to housing degradation, and forms a channel for moisture absorption, through which Ag plating on the lead frame can be oxidized and sulfurized. This oxidation and sulfurization leads to a drop in reflectance with a decrease in light intensity. The oxidation and sulfurization also reduces the adhesion between the lamp house (package 101) and the lead frame 104, causing problems in moisture resistance and reflow resistance.
As described above, the diagonal LED of PLCC type shown in FIG. 1 cannot solve the problem of springback due to the cutting and forming of the lead frame, or the problem of the miniaturization limit of the molding resin.